Systems and methods for providing percutaneous electrical stimulation

ABSTRACT

Systems and methods according to the present invention relate to a novel peripheral nerve stimulation system for the treatment of pain, such as pain that exists after amputation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/440,784, filed Apr. 5, 2012, and entitled “Systems and Methods forProviding Percutaneous Electrical Stimulation,” which claims the benefitof U.S. Provisional Patent Application No. 61/472,063, filed Apr. 5,2011, and entitled “ Systems and Methods for Providing PercutaneousElectrical Stimulation”, which are hereby incorporated by reference.U.S. patent application Ser. No. 13/440,784 is a continuation-in-part ofU.S. patent application Ser. No. 12/462,384, filed Aug. 3, 2009, andentitled “Portable Assemblies, Systems, and Methods for ProvidingFunctional or Therapeutic Neurostimulation,” which claims the benefit ofU.S. Provisional Patent Application No. 61/137,652, filed Aug. 1, 2008,and entitled “Portable Assemblies, Systems, and Methods for ProvidingFunctional or Therapeutic Neurostimulation,” is also acontinuation-in-part of U.S. patent application Ser. No. 12/653,029,filed Dec. 7, 2009, and entitled “Systems and Methods To Place One orMore Leads in Tissue for Providing Functional and/or TherapeuticStimulation,” which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/201,030, filed Dec. 5, 2008, and entitled“Systems and Methods To Place One or More Leads in Tissue for ProvidingFunctional and/or Therapeutic Stimulation,” is also acontinuation-in-part of U.S. patent application Ser. No. 12/653,023,filed Dec. 7, 2009, and entitled “Systems and Methods To Place One orMore Leads in Tissue to Electrically Stimulate Nerves of Passage toTreat Pain,” which is incorporated herein by reference in its entiretyand which claims the benefit of U.S. Provisional Patent Application No.61/201,030, filed Dec. 5, 2000, and entitled “Systems and Methods ToPlace One or More Leads in Tissue for Providing Functional and/orTherapeutic Stimulation,” and is also a continuation-in-part of U.S.patent application Ser. No. 13/323,152, filed Dec. 12, 2011, andentitled “Systems and Methods for Percutaneous Electrical Stimulation,”which is a continuation of U.S. patent application Ser. No. 13/095,616,filed Apr. 27, 2011, and entitled “Systems and Methods for PercutaneousElectrical Stimulation,” which claims the benefit of U.S. ProvisionalPatent Application Ser. No. 61/343,325, filed Apr. 27, 2010, andentitled “Systems and Methods for Percutaneous Electrical Stimulation,”all of which are hereby incorporated by reference.

Every combination of the various embodiments contained in theincorporated reference applications may be formed so as to carry out theintention of embodiments of the invention described below.

BACKGROUND OF THE INVENTION

Approximately 185,000 individuals in the U.S. undergo an amputation eachyear. The majority of new amputations result from vascular disorderssuch as diabetes, with other causes including cancer and trauma. Almostall amputees (95%) have intense pain during the recovery periodfollowing their amputation, either sensed in the portion of the limbthat remains (residual limb pain) or in the portion of the limb that hasbeen removed (phantom pain). It is critical to treat this sub-chronicpain condition quickly and effectively to avoid the significant social,economic, and rehabilitation issues associated with severepost-amputation pain. Other types of neuropathic pain affect over 6million Americans.

Almost all amputees (95%) have pain related to their amputation:approximately 68-76% of amputees have residual limb pain (RLP) and72-85% of amputees have phantom limb pain (PLP). Their severity andprevalence make them significant medical problems. Pain can lead todiscouragement, anger, depression, and general suffering. PLP and RLPfrequently cause further disability and greatly reduce quality of life(QOL). In amputees with severe pain, it is frequently the pain ratherthan the loss of a limb that most impacts daily activities andemployment. Amputee pain has a significant economic impact on thepatient and society. For the patient, the median cost of medicationsexceeds $3,000/year and the median cost for a treatment regimen providedby a pain management center is over $6,000/year. The annual cost in theU.S. to manage post-amputation pain is estimated to be over $1.4 billionfor medications and over $2.7 billion for pain center treatmentprograms. When the overall costs of pain management care are summed, theannual cost can exceed $30,000/patient for a cost of over $13billion/year to treat amputees with severe pain in the US.

Present methods of treatment are unsatisfactory in reducing pain, haveunwanted side effects, and are not suited for temporary use. Electricalstimulation of nerves can provide significant (>50%) pain relief, butpresent methods of implementation are either inappropriate forsub-chronic pain due to their invasiveness, or are uncomfortable andinconvenient to use. We have developed an innovative, minimally invasivemethod of delivering temporary electrical stimulation to target nerves.Preliminary data on treating amputee pain using methods according to thepresent invention are promising, but there is a significant need for astimulation system that overcomes the technical and clinical barriers ofpresently available devices, including imprecise programming (requiringprecise lead placement which is impractical for widespread use) and lackof moisture ingress protection (requiring removal of system during somedaily activities).

PLP and RLP are severe and debilitating to a large proportion ofamputees, who often progress through a series of treatments withoutfinding relief. Most patients are managed with medications. Non-narcoticanalgesics, such as non-steroidal anti-inflammatory drugs (NSAIDS), arecommonly used but are rarely sufficient in managing moderate to severepain. Trials of narcotics have failed to show significant reduction inPLP, and they carry the risk of addiction and side effects, such asnausea, confusion, vomiting, hallucinations, drowsiness, headache,agitation, and insomnia. Other medications such as antidepressants areused for neuropathic pain, but their use for post-amputation pain isbased primarily on anecdotal evidence and there are few controlledclinical trials to support their efficacy for post-amputation pain.Physical treatments (e.g., acupuncture, massage, heating/cooling of theresidual limb) have limited data to support their use and are not wellaccepted. Psychological strategies, such as biofeedback andpsychotherapy, may be used as an adjunct to other therapies but areseldom sufficient on their own, and there are few studies demonstratingtheir efficacy. Mirror-box therapy has demonstrated mixed results and isnot widely used. Few surgical procedures are successful and most arecontraindicated for the majority of the amputee patients 11. Studieshave shown that pain resolves over the first 6 months followingamputation for some patients. Within 6 months, RLP resolves for 60% ofpatients and PLP resolves for 10% of patients, with another 40%experiencing a significant reduction in pain intensity, making itinappropriate to use invasive methods before establishing that the painis long-term (>6 months).

Prior electrical stimulation has been attempted. Transcutaneouselectrical nerve stimulation (TENS, i.e., surface stimulation) is acommercially available treatment and has been demonstrated at being atleast partially successful in reducing post-amputation pain. However,TENS has a low (<25%) success rate due to low patient compliance.Patients are non-compliant because the stimulus intensity required toactivate deep nerves from the skin surface can activate cutaneous painfibers leading to discomfort, the electrodes must be placed by skilledpersonnel daily, and the cumbersome systems interferes with dailyactivities. Spinal cord stimulation (SCS), motor cortex stimulation, anddeep brain stimulation (DBS) have evidence of efficacy, but theirinvasiveness, high cost, and risk of complications makes theminappropriate for patients who may only need a temporary therapy. Highfrequency nerve block has been shown to decrease transmission of painsignals in the laboratory, but the therapy has not been developed forclinical use. Historically, peripheral nerve stimulation (PNS) for painhas not been widely used due to the complicated approach of dissectingnerves in an open surgical procedure and placing leads directly incontact with these target nerves. Such procedures are time consuming andcomplex (greatly limiting clinical use outside of academicinstitutions), have risks of damaging nerves, and often (27%) haveelectrode migration or failure. Other groups are developing percutaneouselectrode placement methods, but their methods still require delicate,placement and intimate contact with the nerve, making them prone tocomplications and migration (up to 43%) because the technology lackssufficient anchoring systems, leading to loss of pain relief and rapidfailure (averaging 1-2 revisions/patient).

SUMMARY OF THE INVENTION

A system according to the present invention relates to a novel,non-surgical, non-narcotic, minimally-invasive, peripheral nervestimulation pain therapy intended to deliver up to 6 months or more oftherapy to patients that may be experiencing pain, such aspost-amputation pain. In one embodiment, system components are anexternal stimulator, preferably a 2-channel stimulator that connects toup to two percutaneous leads, a charging pad for recharging thestimulator, and wireless controllers used by the patient and theclinician.

Systems and methods according to the present invention overcome at leastthe limitations or drawbacks of conventional TENS systems, such ascutaneous pain and low compliance, thought to be at least partially dueto the cumbersome nature of prior systems. Systems and methods accordingto the present invention also overcome at least some of the limitationsor drawbacks of conventional surgical options such as SCS, DBS, andsurgically-implemented PNS, such as invasiveness, cost, and risk ofcomplications. Systems and methods according to the present inventionrelate to delivering stimulation percutaneously (electrical currenttraveling through a lead placed through the skin) which has significantadvantages. Such stimulation may be provided using methods that areminimally invasive and reversible (making it ideal for treatingtemporary pain), easy for pain specialists to perform (due to itssimilarity to common procedures such as injections), and can be trialedwithout long-term commitment. In addition, the electrodes of theelectrical leads only need to be placed within centimeters of the nerve,reducing the risk of nerve injury (as the electrode does not touch thenerve) and making the lead placement procedure simple for non-surgeons.Finally, improved percutaneous leads have a proven anchoring system,reducing susceptibility to electrode migration. At the conclusion ofuse, the lead is removed by gentle traction. Systems and methodsaccording to the present invention may employ a percutaneous lead with along history of successful use is multiple pain indications includingamputee pain. Data suggest that systems and methods according to thepresent invention will have a low risk of complications. For instance,in a long-term study of 1713 leads placed in the lower extremities andtrunk, there were 14 (0.9%) electrode fragment-associated tissuereactions that resolved when the fragments were removed with forceps,and 14 (0.9%) superficial infections that resolved when treated withantibiotics and/or the lead was removed.

Ongoing studies are being used to investigate the safety & efficacy oftreating amputee pain using percutaneous leads connected to surfacestimulators to deliver safe stimulation percutaneously, and the resultsare promising. Five subjects with amputations have received in-clinic(i.e., trial) therapy. Three subjects had amputations due to trauma, onedue to cancer, and one due to vascular disease. The subjects had usedvarious combinations of medications (narcotic and non-narcotic),physical therapy, injections, and nerve blocks in the past withoutsuccess. Stimulation was delivered to the femoral nerve (n=1), thesciatic nerve (n=1), or both (n=3) depending on the location of pain. Ofthe three subjects who reported RLP at baseline, the average reductionin pain during in-clinic trial was 64%. The two subjects who reportedPLP at baseline reported a 60% reduction in pain during the in-clinictesting. One subject did not report pain relief due to vasculardysfunction in the amputated limb. It was determined that the nerveswould not respond to stimulation during the in-clinic testing and removethe lead through gentle traction. If this patient had received a trialstage system for SCS, the leads would have required open surgery forremoval. The present approach allows for minimally-invasive screening ofpatients to determine responders. Thus far, three subjects have receivedthe therapy at home for 2 weeks. All three subjects reported significantpain relief for the duration of therapy use. There have been no adverseevents to date. Results are promising, but using prior available surfacestimulators to deliver stimulation through percutaneous leads hassignificant limitations (e.g., per pulse charges that can be unsafe withpercutaneous leads if not limited by a technical modification, lack ofmoisture ingress protection forcing subjects to remove the system whenshowering, burdensome cables that can snag), making it unfeasible todeliver therapy, under methods according to the present invention, usingexisting systems for a full 6-month period. Systems and methodsaccording to the present invention address unfortunate shortcomings ofprior systems, as they may be used to deliver optimal safe and effectivepercutaneous stimulation that will maximize clinical benefit.

Prior systems and methods fail to provide an effective and minimallyinvasive treatment option for patients with post-amputation pain,forcing many of them to suffer with severe pain during their initialrecovery or resort to an invasive therapy that may not be necessary inthe long-term. Systems and methods according to the present inventionhave the capability to provide a therapy that has the potential for ahigh rate of efficacy with minimal side effects, has a simple procedureperformed in an outpatient setting, is temporary & reversible, and hasestablished reimbursement coding and coverage policies (existing codesand coverage policies reimburse the therapy cost and make the procedureprofitable for the hospital % physician). Systems and methods accordingto the present invention may be used to treat other types of neuropathicpain, such as complex regional pain syndrome (CRPS). CRPS is challengingto treat due to its poorly understood pathophysiology, and few patientsreceive pain relief from available treatments. PNS produces dramaticpain relief in most patients with CRPS, but existing methods requiresurgically placing the lead in intimate contact with the nerve. Theseprocedures are time consuming & complex (greatly limiting clinical useoutside of academic institutions), have risks of nerve damage, and often(27%) have lead migration or failure. Another neuropathic pain that maybe treated with systems and methods according to the present inventionis post-herpetic neuralgia, which is severe but often temporary, makinginvasive surgeries inappropriate. Pain due to diabetic neuropathy, whichis poorly controlled using medications, may also be treated usingsystems and methods according to the present invention. As indicated,over 6 million Americans suffer from neuropathic pain, resulting in anegative impact on quality of life (QOL) and profound economic costs.Systems and methods according to the present invention may change howneuropathic pain is managed by providing clinicians with aminimally-invasive, simple, reversible, and effective treatment option,resulting in a significant, decrease in the socioeconomic consequencesof neuropathic pain and an improvement in the QOL of millions ofAmericans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 depict a preferred external stimulator according to thepresent invention.

FIGS. 8-11 depict a preferred mounting patch according to the presentinvention.

FIG. 12 shows a partial assembly view of an external stimulator andmounting patch according to the present invention.

FIGS. 13-19 depict the stimulator from FIGS. 1-7 coupled to the mountingpatch from FIGS. 8-11, including the mechanical and/or electricalengagement of the snap receptacles provided on the stimulator with thesnaps provided on the mounting patch.

FIG. 20 depicts a first stimulator controller according to the presentinvention, which may be used by a patient or clinician to preferablywirelessly program and/or control the stimulator of FIGS. 1-7 before orafter the stimulator is supported on a patient, such as by the mountingpatch of FIGS. 8-11.

FIG. 21 depicts a second stimulator controller according to the presentinvention, which may be used by a patient or clinician to preferablywirelessly program and/or control the stimulator of FIGS. 1-7 before orafter the stimulator is supported on a patient, such as by the mountingpatch of FIGS. 8-11.

FIG. 22 is a partial assembly view including an external stimulator,mounting patch, and stimulating lead according to the present invention.The stimulating lead may have one or more stimulating electrodessupported thereby.

FIG. 23 is an assembled view of the embodiment of FIG. 22.

FIG. 24 is a perspective view of the stimulator of FIGS. 1-7 resting onan inductive charging mat, which is preferably connected to a powermains.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention which may be embodied inother specific structures. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention, which is defined by the claims.

Systems, components, or methods according to the present invention mayprovide safety improvements, such as electrical safety improvements thatmay be provided by improved moisture ingress protection.

Systems, components, or methods according to the present invention mayprovide stimulation output improvements, such as direct-to-nervestimulation and current-controlled output.

Systems, components, or methods according to the present invention mayprovide stimulation usability improvements, such as decreased physicalsize, wireless stimulation control, and decreased maintenancerequirements.

A system according to the present invention may include one or more ofthe following components: an external stimulator, percutaneous leads, apatient controller, a charging pad, and a clinician controller. Theexternal stimulator is a preferably small, lightweight pod that may beselectively mountable to a replaceable adhesive patch that may functionas a return electrode. The external stimulator is preferably less thanfour centimeters wide, less than six centimeters long, and less than onecentimeter thick. More preferably, the external stimulator is about 3.6centimeters wide, about 5.8 centimeters long, and about 0.8 centimetersthick. The external stimulator weighs preferably less than 30 grams, andmore preferably less than 24 grams. The external stimulator may includeor not include a power source. If the external stimulator does notinclude a power source, electrical power is provided to electricalstimulation circuitry housed within the stimulator by a battery that ispreferably provided in the adhesive patch. If the external stimulatordoes house a power source, the power source is preferably a battery thatmay be inductively recharged.

The external stimulator may be physically mounted to and supported by anadhesive patch that may be adhered to the skin spaced from, butpreferably near (preferably less than fifteen centimeters) the exit siteof the percutaneous leads (preferably proximal to a prosthetic limb, ifused). The adhesive patch may provide a mounting location for theexternal stimulator, but may also function as a surface electrode foreither stimulating, as an active electrode, or serving as anon-stimulating return electrode. Thus, the mounting mechanism betweenthe patch and the external stimulator is preferably electricallyconductive, such as one or more metallic snap structures that aremateable with corresponding seat structures provided on the externalstimulator. The patch may provide an additional, alternate, and/orback-up power supply for electrical stimulation circuitry contained inthe external stimulator. A preferred smooth and low profile design ofthe housing of the external stimulator, helps reduce a majority ofcommon problems associated with existing external stimulators, includingaccidental button activation and snagging on clothes (which candisconnect or break the electrodes). Wireless control, such as with aremote controller, allows further miniaturization of the stimulator,decreasing the footprint of the device on the skin surface and allowingit to be worn almost imperceptibly under clothing, in contrast tocommercially available stimulators which are typically worn outside ofclothing due to their large size and the need to view the displayscreen. Using a system according to the present invention, a patient mayutilize a controller, such as a key-fob like device, to adjust theintensity of each percutaneous stimulation channel within a safe andeffective range. Recharging the power source of the stimulator may beperformed in a variety of ways. If a power source is provided in thestimulator housing, the power source is preferably a battery that may beinductively recharged, preferably within 2 hours by placing it on acharging pad. A clinician controller may be provided in the form of anotepad computer with custom software and a wireless communicationsinterface or adaptor for programming stimulus parameters in the externalstimulator or the controller used by the patient, and reading patientcompliance data from the external stimulator or from the controller usedby the patient.

Systems according the present invention are preferably designed to meetpreferred safety, output, and usability goals that are not met bypresently available devices, see Table b.1, below. Safety features suchas maximum per pulse charge safe for percutaneous stimulation, moistureingress protection for safe use during daily activities includingshowering, and limited programming by patients, may be incorporated.Design mechanisms to deliver minimally-invasive and effective therapy,such as bypassing cutaneous pain fibers and current-controlled output,may also be included. Features that improve comfort and usability mayalso be incorporated, such as miniaturization and low maintenance.

TABLE B.1 Systems and methods according to the presert invention addresslimitations of prior available devices. Preferred features of Possiblelimitations of available embodiments of technology (surface stimulatorssystems according to and trial SCS stimulators) present invention SAFETYOutput safe for Surface stimulators can be adjusted Full parameter rangeis stimulus to per pulse charges that can damage safe for use withdelivery via tissue when used with percutaneous percutaneous leadspercutaneous leads, which would be an off-label (preferred maximum perleads use pulse charge injection of 4 μC = 0.4 μC/mm²) Moisture Mostsurface stimulators rated as Rated as IP44 ingress IPX0 (ordinaryequipment). Must be (protection from water protection removed duringdaily activities such sprayed from all suitable for as showering.directions). Remains safe wearing on the and reliable despite skinduring all perspiration, showering, daily activities etc. PatientSurface stimulators allow unrestricted Allows patient to selectadjustment of adjustment, resulting in stimulus from a safe andeffective stimulus output that can be ineffective or range ofintensities with intensity within unsafe minimal clinician a safe &programming. effective range Minimally Trial SCS leads are placed viaopen percutaneous leads are invasive lead procedures requiring imagingplaced through the skin placement by non-surgeons OUTPUT ComfortableSurface stimulation can activate Therapy is delivered therapy (for highcutaneous pain fibers leading to directly to the nerves, compliance)discomfort/pain bypassing cutaneous pain fibers. Current- Many surfacestimulators are voltage- Current-controlled controlled controlled: theoutput current output, eliminating output output to depends on surfaceelectrode-to- variability. minimize tissue impedance which varies overvariability time and by surface, electrode among patients adhesion andcleanliness of skin USABILITY Minimization of Surface stimulatorstypically worn on Elimination of cable cables, low the waist due totheir large size connecting anode. profile, and (typical dimensions of 6cm × 10 cm × Minimization of cable small size 2.5 cm), requiring cablesconnecting connecting cathode by the stimulator to the electrodes on theplacing system on skin skin. Cables interfere with daily near lead site.Preferably activities and restrict movement. sized approx. 3.6 cm × 5.8cm × 0.8 cm and 24 g. Ease of Patients must open the battery Rechargedby placing it recharging and compartment of surface stimulators on arecharging pad, an low and replace the battery regularly. This actionthat can he done maintenance can be difficult for patients with with onehand. impairments. Surface electrodes must Percutaneous lead is beplaced by skilled personnel daily. placed once.

Previous and ongoing studies suggest that PNS can significantly reducepost-amputation pain, but a system capable of delivering minimallyinvasive therapy safely and effectively does not exist. Systems andmethods according to the present invention provide an innovative PNSsystem that addresses deficiencies in presently available devices inaddition to introducing features that will improve the experience forthe patient and clinician. Such systems and methods will improveclinical practice for pain management by providing clinicians with atherapy that can significantly reduce pain following amputation andimprove QOL during the first 6 months of recovery without systemicside-effects or invasive procedures. For many amputees, pain subsidesover time and the systems and methods according to the present inventionmay be the only pain therapy necessary. For patients who continue toexperience pain, either the therapy can be re-dosed or a fullyimplantable electrical stimulation system can be considered.

Preferred technical features of a system according to the presentinvention include preferred stimulation parameters, electrical safety(including reduction of moisture ingress), physical characteristics, andoperational functionality. Regarding stimulation parameters, a preferredstimulation amplitude is in a preferred range of about 0-30 milliamps,and more preferably in a preferred range of 0.1 mA-20 mA, +/−7%. Apreferred pulse duration is about 0-500 microseconds, and morepreferably is a range of 10-300 microseconds, +/−2-30%, but morepreferably +/−2%. The pulse duration is preferably adjustable inincrements of a single microsecond, though a coarser adjustment such as10's of microseconds may be provided. A preferred stimulation frequencyis in the range of about 0-500 Hz, and more preferably in a range of1-200 Hz, +/−1-30%, but more preferably +/−1%.

Preferred electrical safety features include single-fault conditionsafety conditions that are generally standard to neurostimulationsystems, but may also include improved, reduced moisture ingressresistance, which allows the external stimulator to be worn at alltimes, even during a shower, for example, and yet remain safe andreliable.

Preferred physical characteristics include relatively small size andmass for an external electrical stimulator. Preferred dimensions of thestimulator housing are about 3.6 centimeters×about 5.8 centimeters×about0.8 centimeters. A preferred mass is about 24 grams.

Regarding operational functionality, an external stimulator according tothe present invention is preferably controllable and/or programmable viaa wireless interface that may be a radio interface, such as a Bluetoothinterface or other RF interface, or an infrared communicationsinterface. Whatever wireless protocol is selected, it is preferred that,upon command to transmit a control signal to the stimulator, such asfrom a controller manipulated by a patient or clinician, the action maybe performed by the stimulator within one second. Wirelessprogrammability and/or control allows for stimulator miniaturization.Stimulator miniaturization allows a low profile housing to enable a userto carry on and perform daily activities with limited concern ofinterfering with therapy provided by the stimulator, and further allowsthe user to keep the stimulator out of view, such as under clothing.Also regarding operational functionality, preferred stimulatorsaccording to the present invention have an operating life of at leastone week at maximum settings used for RLP and PLP with stimulationsettings at 5 mA amplitude, 20 microsecond pulse width and 100 Hzfrequency. Such preferred operational functionality provides a user withat least one week without the need to recharge or replace a power sourceof the stimulator. Additionally, as already mentioned an operationallycomplete battery charge is preferred to occur in less than or equal totwo hours of time.

Optimal stimulation of peripheral nerves for pain relief usingpercutaneous leads is most efficient through the generation and use of acontrolled current, biphasic stimulus output with no net direct current(DC) and accurate stimulus parameters with precise programming. This maybe accomplished through the use of circuit topologies and componentscapable of the required precision and stability despite changes inbattery voltage, operating temperature, and aging. These requirementsare easily achieved with conventional instrumentation design methods;however, these design methods are often at conflict with miniaturizationand minimal power consumption (i.e., maximum battery life), which areboth key features of a comfortable and easy to maintain externalstimulator. To overcome this issue, precision circuit components andtopologies may be used to ensure that the required accuracy andprecision are achieved. Also, multiple power reduction methods may beused, such as disabling the portions of stimulation circuitryresponsible for controlling the stimulus current between stimuluspulses, specifying fast turn-on voltage reference semiconductors,enabling them only shortly before use, and disabling them as soon astheir measuring or output function is completed. These powerminimization features may be implemented in the embedded software of thestimulator (i.e., in firmware of a microcontroller of the circuit boardassembly).

Regarding an aspect of electrical safety, the electrical stimulationcircuitry in the external stimulator preferably monitors total currentdrawn from the stimulus power supply. An excessive load, indicated by ahigh current draw, on this power supply may be caused by a componentfailure or a failure of the enclosure to isolate the circuitry frommoisture and hazard currents through the compromised enclosure. When ahigh current or an excessive load is detected, the stimulator and/orpower supply are shutdown, preferably within 100 milliseconds, and morepreferably within 50 ms. confirming appropriate failsafe response.

Also related to electrical safety, and general reliability, is moistureingress protection. It is preferable to ensure that the stimulatorcircuitry not damaged or made unsafe by moisture ingress. The technicalchallenges of packaging electronics for reliable operation in moistenvironments have been solved in numerous scientific, military,industrial and commercial applications, but the additional requirementsof minimizing size and weight increase the technical burden. To achievea safe reliable stimulator in a potentially moist environment, it ispreferable to 1) eliminate or substantially reduce unnecessary seams inthe molded plastic enclosure (e.g., switches, displays, battery accesspanel); 2) use sealed electrical connectors for the two-channelpercutaneous lead receptacle and the snap connectors to the surfacereturn electrode; and 3) provide a mechanism to allow venting theenclosure without providing a path for the ingress of fluids. Apreferred stimulator housing is capable of preventing the ingress ofwater when sprayed from any direction at the housing for 10 minutes withspecified flow rates and pressure. Note that the electrical safetyfunction provided by the enclosure is single fault tolerant given thefail-safe stimulation power supply circuitry described above. Additionalmoisture control mechanisms may be employed such as conformal coatingthe circuit board and/or using a moisture getter (desiccant) inside thestimulator housing.

Patient comfort may be optimized by a stimulator and/or controller thatare as small and light as possible. The stimulator preferably isapproximately 3.6×5.8×0.8 cm and about 24 g. One way that such size maybe achieved is by employing a button-less stimulator. Rather than havingcontrols on the stimulator, a key-fob like controller containing adisplay and controls may be used by a patient or clinician to operateand/or program the stimulator, eliminating the size and weightassociated with these elements (and increasing its integrity againstmoisture ingress). Lustran 348 ABS plastic is an exemplary material forthe stimulator housing material for an optimal strength to weight ratio,durability and impact resistance, ease of fabrication, and evidence ofbiocompatibility. Internal rib structures may be incorporated into thedevice top housing to position and support the rechargeable lithium ionbattery, circuit assembly, and recharging coil. The housing preferablyhas a smooth surface that is tapered at the periphery to minimize thepotential for snagging. The top and bottom housing are preferably joinedusing an ultrasonic welding operation in order to ensure protectionagainst water ingress, which may have the added features of eliminatingthe presence of thru-holes or lock-tabs frequently used for assembly ofplastic housings of prior external stimulators. The size of the circuitassembly is preferably minimized through high-density circuit design andfabrication methods. FIG. 12 shows the internal construction of thestimulator, adapted to fit within a preferred target stimulator size.

Regarding control and/or programmability of the external stimulator, theuse of a limited range wireless personal area network (PAN)communications system may be used to the utility of the stimulatorbecause it eliminates the need for the patient to access the stimulatorto start, stop, or adjust the intensity of the stimulation. The patientuses a small (i.e., 5.2×3.0 a 0.8 cm) wireless controller to control thestimulator and retrieve information from the stimulator (e.g., batterycharge status, stimulus intensity). The clinician controller, such as atablet PC, also uses the wireless link to retrieve usage information andto program stimulus settings. Driven by the rapid growth of short rangewireless PANs in personal devices (e.g., cell phone head sets, remotecontrols for televisions, personal fitness and health monitoringdevices), a number of micro-power wireless radio chip sets (i.e.,integrated circuits specifically designed for short range communicationsat very low power levels) have become available with software forseveral low power communications protocols. Various chip sets and/orprotocols may be used to implement a wireless telemetry link. The use ofreadily available chip sets and reference designs may significantlyreduce the design effort required and the associated technology risksand ensure a ready source of low cost integrated circuits. Preferred areparameters such as performance levels (communications range (1 m infront of patient with stimulator anywhere on patient), interferencerecovery (using the standard test methods and limits of the protocolselected), peak and average current consumption (consistent with theselected battery capacity and operating life), and message quality andlatency time (i.e., preferably at least 95% of all patient initiatedcommands are received and acted on by the stimulator within 1 second).

Using a computer model of stimulator battery current consumption, thebattery capacity was estimated for the stimulation circuitry to operateat the maximum optimal levels used to date during clinical trialinvestigations of peripheral nerve stimulation for post-amputation pain(5 mA, 20 μsec, and 100 Hz on each of the two stimulation channels).With a battery capacity of 100 mA-hours, the stimulator preferably hasno need to be recharged more than once every eight days or so. Therechargeable battery may be formed from one or more Lithium Ion Polymercells, preferably each that has 120 mA-hr or more of capacity, meet thepackage constraints, and preferably uses less than 25% of the availablepackage volume. A commercially available charging pad compliant with theWireless Power Consortium standard such as the Energizer®. InductiveCharger may be used.

Preferably, the external stimulator with adhesive patch may becomfortable to wear on the body for 24 hours/day. The adhesive patchpreferably adheres securely to a skin surface of a human body for atleast 24 hours.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and operation shown anddescribed. While the preferred embodiment has been described, thedetails may be changed without departing from the invention, which isdefined by the claims.

We claim:
 1. A system comprising: a patch member having an adhesivedisposed on a first side and a patch mounting structure disposed on asecond side, opposite the first side, and an electrically conductivereturn electrode material disposed between the first side and the secondside; an electrical stimulation device comprising: a housing havingoppositely disposed, substantially planar top and bottom surfaces,wherein the top surface is imperforate; a device mounting structure onthe bottom surface physically mated with the patch mounting structure;electrical stimulation generation circuitry disposed at least partiallywithin the housing; one or more of a rechargeable battery, an inductivecharging circuit adapted to receive an inductive charging signal, and awireless communication module adapted to receive wireless communicationsto select or a stimulation pattern to be generated by the electricalstimulation circuitry; an electrode electrically coupled to theelectrical stimulation generation circuitry.
 2. A system according toclaim 1, wherein the top surface and the bottom surface of the housingare separated by a device thickness, wherein the housing furthercomprises a perimeter edge extending from the bottom surface and asloped interface edge connecting the top surface to the perimeter edgealong a majority of the perimeter thereof wherein the height of theperimeter edge, measured perpendicular to the top and bottom surfaces,is less than the device thickness.
 3. A method of treating bodily painof an animal comprising the steps of: providing a patch member having anadhesive disposed on a first side and a patch mounting structuredisposed on a second side, opposite the first side, and an electricallyconductive return electrode material disposed between the first side andthe second side; providing an electrical stimulation device comprising:a housing having oppositely disposed, substantially planar top andbottom surfaces, wherein the top surface is imperforate; a devicemounting structure on the bottom surface configured to physically matewith the patch mounting structure; electrical stimulation generationcircuitry disposed at least partially within the housing; one or more ofa rechargeable battery, an inductive charging circuit adapted to receivean inductive charging signal, and a wireless communication moduleadapted to receive wireless communications to select a stimulationpattern to be generated by the electrical stimulation circuitry;coupling the electrical stimulation device to the mounting structure;adhering the patch member to a skin surface of the animal; implanting anelectrode in subcutaneous bodily tissue of the animal; electricallycoupling the electrode to the electrical stimulation generationcircuitry; generating electrical stimulation using the electricalstimulation generation circuitry; delivering the electrical stimulationto the bodily tissue; observing whether the electrical stimulation atleast partially relieved the bodily pain.
 4. A method according to claim3, wherein the bodily pain is bodily pain existing in the body of thepatient after an amputation of a body part.
 5. A method according toclaim 4, wherein the bodily pain did not exist prior to the amputation.6. A method according to claim 5, wherein the bodily pain existed priorto the amputation, but was absent prior to trauma inflicted upon thebody part.